1. Field of the Invention
The present invention relates to a medical device which closes a defect occurring in a living body and particularly to an improvement of electrode members sandwiching a biological tissue.
2. Description of the Related Art
Recently, a patent foramen ovale (hereinafter, referred as to PFO: Patent Foramen Ovale) has been cited for a cardiogenic factor of a stroke and a hemi headache. A PFO is a symptom in which a foramen ovale which makes blood shunt for the right to the left in the heart of a fetal period remains even if a fetus becomes adult and it is said that 20 to 30% of adults possess it.
The foramen ovale occurs at a septum secundum (Septum Secundum, hereinafter, referred to as atrial septum) of the heart and the pressure on the left atrium side exceeds the pressure on the right atrium side in the heart on a normal occasion, so that it is occluded by a septum primum (Septum Primum, hereinafter, referred to as foramen ovale valve), but when the pressure on the right atrium side exceeds the pressure on the left atrium side on a strain occasion (for example, when coughing, when holding on) or the like, the foramen ovale valve opens to the left atrium side and it happens that blood flows from the right atrium side (venous side) into the left atrium side (arterial side). When a thrombus is included in this blood, it happens that the thrombus is shifted from the venous side to the arterial side, flows in a route of left atrium →left ventricle→aorta→brain, and it becomes a factor for a stroke, hemi headache or the like.
For a treatment with respect to such a disease, a treatment by a percutaneous catheter procedure is considered to be a desirable method if the same effect as an open heart surgery can be obtained.
A device of a closing technique using the percutaneous catheter can be used also in case of closing defects such as a congenital atrial septum defect (ASD), a PFO, a ventricular septal defect (VSD) and a patent ductus arteriosus (PDA), and the conventional device is a device sandwiching the foramen ovale valve and the atrial septum by using disk-shaped membranes or anchor members for closing the defect and these are detained in the body.
The membranes or anchor members are foreign substances for a human body and moreover, a thrombus is easy to be attached. In particular, when a thrombus is attached on a disk-shaped membrane or the like on the left atrium side, this flows and there is a possibility that it becomes a cause of a stroke, and there is also a fear that a foramen ovale valve of a thin wall thickness is broken. In addition, these members are not position-fixed in a state of being sandwiched and there is also a possibility of causing a positional displacement.
Consequently, recently, there has been proposed a PFO closing device described in WO2004/086944 A2. This PFO closing device is an apparatus inserted into the foramen ovale from the right atrium toward the left atrium, a foramen ovale valve is pulled to the foramen ovale so as to close it and the tissue is to be inosculated by applying electric energy. However, the foramen ovale, the foramen ovale valve and the atrial septum are different not only in small/large sizes but also in a condition of thicknesses, shapes or the like depending on persons and according to circumstances, it happens that the size or the like of the apparatus is restricted a lot. Also, even on an occasion when the procedure is performed, there is a fear that it becomes difficult to pull various forms of foramen ovale valves to the foramen ovale at anytime and certainly.
Consequently, it is also possible to suture the tissue by sandwiching the foramen ovale valve and the atrial septum using a pair of electrodes and by applying electric energy from both the electrodes. However, when electric energy is applied to the biological tissue in the blood in a state in which the electrode is exposed, a thrombus is generated at the periphery of the electrode depending on circumstances. In particular, it sometimes happens that the biological tissue is contracted by receiving thermal influence. When the biological tissue is thermally contracted, there is also a fear that the proximal side of the electrode member contacting with the biological tissue is exposed and a thrombus will attach on this exposed portion.